The classic vibes of the 1960s “San Francisco Sound” were resonating across the decades this May, still coming through loud and clear. Phil Lesh of the Grateful Dead was headlining a five-night run at San Francisco’s Warfield Theater, while the off-night of the run saw no less than GD contemporaries Jack Casady and Jorma Kaukonen of Hot Tuna (and Jefferson Airplane fame) bringing their own classic rock stylings to the Great American. How fitting (and lucky for fans) that the schedules of these ’60s rock pioneers would co-mingle once again four decades later. Back in the ’60s, Kaukonen and Casady provided much of the punch that drove the musical engine of Jefferson Airplane, who at the time were just as big as The Dead. The duo splintered away from The Airplane in the early ’70s to pursue a more jam-oriented sound and while their bandmates seem to have unfortunately faded away, Hot Tuna is still going strong. In fact, bassist Casady and guitarist Kaukonen are celebrating 50 years (!) of partnership this year, having played together off and on since they were teens. There are few collaborations in rock ‘n’ roll that have reached a golden anniversary, so it’s a true treat for the packed house to take in such a show. It’s an electric quartet tonight, with Erik Diaz on drums and Barry Mitterhoff on mandolin and guitar rounding out the lineup. The band opens with “Serpent of Dreams”, and there’s a confident chemistry that’s clearly present from the start. Many bassists are playing five- or even six-string instruments these days, but Casady is still plucking a classic four-string semi-hollow body bass, and it sounds so good. There’s a deep blues vibe, and Casady’s notes are powerful yet smooth. Kaukonen, meanwhile, weaves his lines in and out with an expert touch– the duo operating almost as if by one mind. Kaukonen’s tone is masterful — whether it’s bluesy, harder rocking, or mellow, his sound always seems just right. The show kicks into high gear with “Living Just for You”, a melodic rocker that gets the whole place moving. It’s the type of sweet groove that could work in any decade, and even those fans who had seemed low on energy suddenly find themselves up and dancing to the infectious groove. Casady and Diaz rock the low end with tight precision, while Kaukonen and Mitterhoff deliver the melodic lines that carry the tune out of the park. There’s a definite magical vibe in the air, connecting 2008 with 1968 and all the music in between. Listening to Kaukonen’s smoking solo over Casady’s compelling groove, a Jefferson Airplane fan can’t help but wonder what Paul Kantner and the others could have possibly been thinking when they let Casady and Kaukonen walk away. Mitterhoff fits right in throughout, alternating between mandolin and a little four-string guitar. He leaves the warm lead guitar sounds in Kaukonen’s capable hands and accents the band’s sound in the higher register. His mandolin work on “I Know You Rider” and “99 Year Blues” fits like a glove. Diaz, meanwhile, is dialed right in with Casady all night long, bashing out a backbeat that never falls out of synch. This leaves the door open for Casady and Kaukonen to follow their muses wherever they may lead, which is into one hot jam after another. “Rock Me Baby” takes the crowd back forty years — the song appeared on Jefferson Airplane’s 1968 live album Bless its Pointed Little Head — and these blues sure have aged well. The Airplane/Hot Tuna version is more like the slower B.B. King original than the turbo-charged Jimi Hendrix version that may be more familiar to some, but the tune remains ripe for the Tuna duo’s classic bluesy explorations. Later, a bass and drums jam between Casady and Diaz conjures a powerful energy that could fit in at a hard rock or metal show. Casady’s driving bass seems to envelop the entire hall, but with a tone that always remains crystal clear, never muddy. The powerhouse jam is another of the evening’s many highlights. Time and again, it’s the energy of Casady and Kaukonen that continually wows the audience. Like his low-end contemporary Lesh, Casady delivers scintillating lead bass lines that would be the envy of most players half his age. The man helped pioneer the lead bass concept, yet like a true master, always knows how to make it serve the song. Kaukonen, meanwhile, maintains a vibrancy in his tone and playing that belies his age. Rock ‘n’ roll must elicit some sort of youth elixir, for these two classic rock warriors sound just as vital in 2008 as they did back in their original heyday. Hail, hail, rock ‘n’ roll.